Aqueous sol and gel of zirconium compounds

ABSTRACT

THE INVENTION DISCLOSES A NOVEL ZIRCONIUM COMPOUND WHEREIN THE RATIO OF NITRATE TO ZIRCONIA IS ABOUT 1.1. THIS COMPOUND IS MADE BY REACTING ZIRCONIUM HYDROXIDE OR CARBONATE WITH NITRIC ACID TO PROVIDE A WATER-BASED SOL. THE SOL MAY BE CONVERTED INTO THE GEL BY DRYING AT ABOUT 80-90*C. OVER A PERIOD OF A FEW DAYS TO GIVE A SOLID GLASSY MASS WHICH CAN EASILY BE RE-DISSOLVED IN WATER TO GIVE THE SOL. THE GEL HAS THE EMPIRICAL FORMULA:   (ZR4(OH)12(NO3)2(H2O)4)(NO3)2.2H2O   AND CONTAINS LATTICE WATER, COVALENT NITRO GROUPS AND IONIC NITRATE GROUPS.

United States Patent M US. Cl. 252313 R 2 Claims ABSTRACT OF THEDISCLOSURE The invention discloses a novel zirconium compound whereinthe ratio of nitrate to zirconia is about 1.1. This compound is made byreacting zirconium hydroxide or carbonate with nitric acid to provide awater-based sol. The sol may be converted into the gel by drying atabout 80-90 C. over a period of a few days to give a solid glassy masswhich can easily be re-dissolved in water to give the sol. The gel hasthe empirical formula:

and contains lattice water, covalent nitro groups and ionic nitrategroups.

This application is a division of my co-pending application Ser. No.643,348, now Pat. No. 3,518,050, issued June 30, 1970.

BACKGROUND OF THE INVENTION The present invention relates to zirconiumcompounds and more specifically to compounds containing zirconium andnitrate ions.

Two zirconium/nitrate compounds are known, namely zirconium nitrateZr(NO -5H O', which may actually be (ZrO) -H (NO -4H O, and a basicnitrate (zirconyl nitrate) ZrO(NO -2H O. It will be observed that inthese compounds the molar ratio (N0 :Zr is 4:1 and 2:1 respectively.

SUMMARY OF THE INVENTION According to the present invention there isprovided a new composition of matter comprising a water-based solcomprising zirconium and nitrate ions, wherein the nitrate to zirconiummolar ratio is 1.1.

The compound may be prepared as an aqueous solution or sol and also in asolid form by drying such solution or sol, this solid form beingre-dispersible in water. Since the liquid form appears to be more in thenature of a sol than a true solution, the term sol will be used herein;by analogy the term gel is used for the solid form.

The compound appears to contain the known cyclic tetramer (Zr (OH)present in so-called zirconyl compounds. This tetramer is believed to bepresent in zirconyl nitrate of empirical formula ZrOONOQ -ZH O for whichwe have obtained the following infra-red data This information confirmsthat zirconyl nitrate contains no lattice water and covalent nitratogroups and can be formulated as [ZI' (O )s( O3) (H O) 3,645,910.Patented Feb. 29, 1972 bridges. If these are equal in number thecompound can be written:

The preferred method of preparation of a sol of the compound of thepresent invention is to prepare a dispersion or slurry of zirconiumhydroxide and react this with an approximately equimolar quantity ofconcentrated nitric acid. The reaction is conveniently carried out atabout 50-70 C. and agitation is desirable. The carbonate may also beused.

it should be observed that commercial zirconium hydroxide and carbonatecontain hafnium and the carbonate contains sodium but these elements donot appear to interfere with the preparation of the sol or gel.

An alternative method of preparation is to heat basic zirconium nitratein air at about 200 C. Provided that the heating is continued for thetime necessary to produce a molar ratio (N0 :Zr of 1.1, the product iscompletely soluble.

Another method of preparation is to prepare zirconium hydroxide and washit well with water. It may then be taken up with basic zirconium nitrateprovided that the correct quantity of nitrate ion is present.

It must be emphasised again that although the term sol is used herein,the product behaves more nearly like a true solution in many of itscharacteristics. However this depends on the correct molar proportionsof NO zZr.

The following Table 1 shows the effect on viscosity and othercharacteristics of altering this ratio.

TABLE 1 NO /Zr Viscosity (centipoise) 1.03 223 1.04 133 1.06 23.2 1.1018.6

With a ratio below about 1.03 it is extremely diflicult, if notimpossible to form a sol. However since a viscosity below about 30 cp.is desirable to obtain a useable sol, the permissable departure from thenominal value of 1.1 is desirably not more than -0.05. It will also beapparent that as the ratio increases the excess nitrate is accommodatedas conventional zirconyl nitrate. For many purposes this is not adisadvantage except that there is a cost penalty in incorporating thenitrate which must later be removed. Thus, if it is desired to formspheres, as is later described, this is effected by denitration of thesol by an amine to give a ratio of approximately 1.05, gelling takingplace extremely rapidly at this ratio. It will be apparent that ifexcess nitrate is present in the form of zirconyl nitrate, a veryconsiderable excess of amine will be necessary to reduce the ratio tothat at which gelling takes place.

Within these limits, however, the sol of the present invention iscompletely stable even at molarities of 4 and above (the maximumconcentration appears to be about 5 molar) and centrifugation gives noseparation even when carried out at 3700 rpm. for 30 minutes.

Having obtained the sol by one of the routes above described, knownstabilisers for zirconia may be added as nitrates without causingprecipitation of the sol. Thus a few percent by weight (based on thezirconia content) of calcia or yttria (as calcium nitrate or yttriumnitrate) may be added.

The sol may be converted into the gel by the simple process of drying atabout -90 C. over a period of a few days to give a solid glassy masswhich can easily be re-dissolved in water to give the sol.

This gel may be de-nitrated by heating in a suitable calciner at about500 C. and the product is then conveniently calcined at some highertemperature, in air, to give zirconia. The final calcining temperatureshould be chosen having in mind the properties, such as surface area,that are required. The sol of the present invention can also be used toplasticise zirconia to permit it to be extruded.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In order that the presentinvention may more readily be unerstood, certain experiments relating tothe same will now be described.

Experiment 1 1.47 kg. of commercial zirconium hydroxide paste (suppliedby Magnesium Elektron Ltd., Manchester) was taken. About half thezirconium hydroxide was added to 0.40 l. of nitric acid (15.7 M) in astainless steel vessel and the remainder was slurried with 0.60 l. ofdistilled water and the slurry added to the nitric acid, with stirring,over 15 mins. The temperature rapidly reached 70 C. and was held at thatvalue by heating for 1 hour. The zirconium hydroxide used proved onanalysis to contain 35.0% by weight of zirconium and hafnium, whereinthe molar ratio Hf :Zr is approximately 1:85. This procedure made about1.84 l. of sol.

The sol was semi-opaque and absorbed ultra-violet light above 250g. The303, absorption bands due to nitrate ion were distorted indicating thepresence of a large and probably complex molecule.

It was apparent that this sol was extremely stable and no tendency togel was observed. It was also tolerant of added nitrate salts. Theaddition of nitric acid however destroyed the sol, probably by theformation of basic zirconium nitrate, in approximate dependance upon thequantity of added nitric acid. The tolerance to added nitrate salts maybe made use of by the addition of stabilisers for zirconia such ascalcia, yttria or like known oxides, provided that the same are added asa solution of the nitrate.

Experiment 2 The above experiment was repeated using zirconium carbonateand the sol produced appeared to be identical.

Experiment 3 TABLE II M clarity Conductivity (zirconium) (mho/cm.) pH

0.46 3. 1X10" 1. 2 0.90 4. 3X10 O. 9 3.42 6.9)(10- 0. 4

Experiment 4 The sol produced in Experiment 1 was taken and 1 litre wasevaporated to dryness in air at C. over a period of 3 to 4 days to give705 g. of a solid glass-like gel which could be dispersed in waterwithout difliculty to reconstitute the sol. The gel analysed as follows:

Zirconium-43.7 by weight (NO ):Zr-1.06 by moles (H O) :Zr-2.97 by molesPhysical characteristics of the gel that were determined included:

Density2.93 g./ cc.

The gel was subsequently de-nitrated by heating to 500 C. and was thencalcined in air at 900 C. to yield 414 g. of an oxide of density 5.26g./cc. (90.7% theoretical). Calcination of normal zirconium hydroxidegives an oxide of density 2.64 g./cc.

Experiment 5 A further batch of 1 litre of sol from Experiment 1 wastaken and was suspended in 3 litres of an inert support liquid,specifically trichloroethane, and then 0.3 litres of a water-insolubleamine was added slowly. The amine used was Primene J .M.T. (a tertiaryalkyl primary amine) which dissolved in the support liquid. Anirreversible reaction took place between the amine and the nitratecontent of the sol partially to denitrate the sol and produce solidspheres which could not be re-dispersed in water. These spheres werecalcined in air at 900 C. to yield 0.414 kg. of zirconia spheres.

I claim:

1. A composition of matter consisting essentially of a dry glassy gel ofempirical formula such gel containing lattice water, covalent nitrogroups and ionic nitrate groups.

2. A composition of matter consisting essentially of a gel dissolved inwater, said gel having the empirical formula 4( H)12( 3)2( Z )4] 3)2' 2said gel containing lattice water, covalent nitro groups and ionicnitrate groups.

References Cited UNITED STATES PATENTS 3,245,757 4/1966 Klimaszewski23-l02 RICHARD D. LOVER'ING, Primary Examiner US Cl. X.R.

